apps: mosquitto_ctrl: don't hard set paths

In a cross compile environment, these paths will be added elsewhere, and
in a local environment, they should already be covered by the system
compiler.  Simply drop them.

Signed-off-by: Karl Palsson <karlp@etactica.com>

Closes #1831. Thanks to Tristan79 and andreas-kluge.

* Fixed some VS2017 compilation errors and warnings.

Signed-off-by: raspopov <raspopov@cherubicsoft.com>

Otherwise, if the package is not installed, configuration will work, but building will fail.

Signed-off-by: Pierre Hallot <hallotpierre@gmail.com>

Some client/app code also optionally use cJSON, however it won't be found if plugins are disabled.

Signed-off-by: Pierre Hallot <hallotpierre@gmail.com>

CMake Warning (dev) at /usr/share/cmake-3.19/Modules/FindPackageHandleStandardArgs.cmake:424 (message):
  The package name passed to `find_package_handle_standard_args` (CJSON) does
  not match the name of the calling package (cJSON).  This can lead to
  problems in calling code that expects `find_package` result variables
  (e.g., `_FOUND`) to follow a certain pattern.
Call Stack (most recent call first):
  cmake/FindcJSON.cmake:23 (FIND_PACKAGE_HANDLE_STANDARD_ARGS)
  CMakeLists.txt:125 (FIND_PACKAGE)
This warning is for project developers.  Use -Wno-dev to suppress it.

Signed-off-by: Pierre Hallot <hallotpierre@gmail.com>